The present invention relates generally to a magnetic particle clutch and more particularly, to a method of controlling operation of a magnetic particle clutch drivingly connected to a rotary blower, such as a supercharger, for supercharging an internal combustion engine.
As is well known to those skilled in the art, the use of a supercharger to increase or xe2x80x9cboostxe2x80x9d the air pressure in an intake manifold of an internal combustion engine results in an engine having a greater horsepower output capability than would occur if the engine were normally aspirated (i.e., if the piston drew air into the cylinder during the intake stroke of the piston). Conventional superchargers are normally driven by an engine, and therefore, represent a drain on engine horsepower when engine boost is not required. For at least this reason, it is known to provide an engageable/disengageable device, such as a clutch, in series between an input (e.g., a belt driven pulley) and a supercharger.
By way of example only, a typical engagement time of a clutch driven supercharger, as specified by a vehicle manufacturer, is about 0.10 seconds. A substantially longer response time would result in the well known xe2x80x9cturbo lagxe2x80x9d feeling characterized by a time lag between depression of a vehicle accelerator and a point when supercharger boost becomes noticeable, as is inherent in a turbo charger type of engine boost system. On the other hand, response time should not be so fast (when engaging) and so sudden as to result in a large torque spike being imposed upon the engine.
It is well known in the art to provide a supercharger driven by a clutch assembly that operates electromagnetically. Although a supercharger with such a clutch arrangement can operate in a generally satisfactory manner once the clutch is in either the engaged or disengaged state, the known arrangement exhibits certain limitations during xe2x80x9ctransientxe2x80x9d conditions, i.e., as the clutch assembly changes from the disengaged to the engaged state, or vice versa. Electromagnetic clutch driven superchargers are typically ON-OFF type devices that engage abruptly with little or no slipping of the clutch, which results in an undesirable transient load torque on the engine during engagement of the clutch. Depending on the engine speed, as a conventional electromagnetic clutch is engaged, a resulting xe2x80x9cdroopxe2x80x9d in engine speed may be perceived by a driver of the vehicle and may be manifested as an undesirable slowing of the vehicle.
The present invention overcomes the limitations of conventional electromagnetic clutch driven superchargers by providing an improved method and control system for controlling a rotary blower having an input and a pair of blower rotors adapted to be driven by the input.
In accordance with an embodiment of the present invention, the method comprises providing a magnetic particle clutch in series driving relationship between the input and the blower rotors. The magnetic particle clutch includes an input member, an output member and a source of magnetic flux. In the presence of a magnetic field, a magnetically reactive medium disposed between the input and output members is transformed into a torque transmitting coupling that causes the clutch to transition from a disengaged state to an engaged state. The method includes sensing a vehicle parameter and generating a signal operable to engage the clutch in response to the sensed vehicle parameter so that the transition from the disengaged state to the engaged state may be controlled as a function of the sensed vehicle parameter.
A control system is also provided comprising a magnetic particle clutch as described above, at least one sensor for sensing a vehicle parameter, such as a rate of change in throttle position, and a control unit operable to selectively communicate a signal to the source of magnetic flux in response to the sensed vehicle operating parameter.
The present invention advantageously provides an improved supercharger and clutch assembly that exhibits both a variable and controllable engagement and disengagement response time, thus avoiding the ON-OFF characteristics of conventional electromagnetic clutch driven superchargers and the resulting transient overloading of the engine.
Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.